A group III nitride semiconductor typified by gallium nitride (GaN) has a direct transition type band structure in a full spectrum of energy band corresponding to visible region through ultraviolet region, and allows production of highly-effective light emitting device. Therefore, the light emitting diode and laser diode have been studied actively, and light emitting diode from visible region to near-ultraviolet region and blue laser diode, etc. are currently commercialized. In the production of such a device, production techniques for p-type GaN are very important, and good p-type conductivity has been achieved for GaN, in which the hole concentration is 1018 cm−3.
On the other hand, for achieving light emitting diode and laser diode glowing in the deep ultraviolet region of 300 nm or less, it is necessary to attain p-type conduction of a group III nitride semiconductor with high Al content such as a group III nitride semiconductor with composition expressed by AlXGaYInZN (where X, Y, and Z are rational number satisfying a relationship of X+Y+Z=1), which satisfies 1.0>X≧0.5. However, increased Al content makes it very difficult to attain p-type conduction.
The causes may be that activation energy (acceptor level) of acceptor impurity atom increases with increase in Al content, and also that carrier compensation is occurred due to introducing many donor defects in crystals. For example, the acceptor level of Mg in GaN is around 150 meV while the same in AlN is around 500 meV (see Non-Patent Documents 1 and 2). Also, according to Non-Patent Document 3, activation energy (EA) of Mg in AlGaN, in which Al proportion (hereinafter referred to as Al composition) in the group III elements is 70% (where X=0.7 and Z=0 in the above formula), is estimated at around 400 meV, and resistivity value (ρ) is said to follow the following equation as a function of temperature.ρ(T)=ρ0exp(EA/kT)
Non-Patent Document 3 reports that resistivity value of the above sample is 40 Ωcm at 800K, but resistivity value is exponentially increased according to the above equation as temperature decreases, and it goes into a semi-insulating state of 105 Ωcm at around room temperature.
[Non-Patent Document 1] J. Crystal Growth 189 (1998) 528
[Non-Patent Document 2] Appl. Phys. Lett. 89 (2006) 152120
[Non-Patent Document 3] Appl. Phys. Lett. 86 (2005) 092108